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cbtree.c
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136 lines (113 loc) · 3.43 KB
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/*
* crit-bit tree implementation, does no allocations internally
* For more information on crit-bit trees: https://cr.yp.to/critbit.html
* Based on Adam Langley's adaptation of Dan Bernstein's public domain code
* git clone https://github.com/agl/critbit.git
*/
#include "git-compat-util.h"
#include "cbtree.h"
static struct cb_node *cb_node_of(const void *p)
{
return (struct cb_node *)((uintptr_t)p - 1);
}
/* locate the best match, does not do a final comparison */
static struct cb_node *cb_internal_best_match(struct cb_node *p,
const uint8_t *k, size_t klen)
{
while (1 & (uintptr_t)p) {
struct cb_node *q = cb_node_of(p);
uint8_t c = q->byte < klen ? k[q->byte] : 0;
size_t direction = (1 + (q->otherbits | c)) >> 8;
p = q->child[direction];
}
return p;
}
/* returns NULL if successful, existing cb_node if duplicate */
struct cb_node *cb_insert(struct cb_tree *t, struct cb_node *node, size_t klen)
{
size_t newbyte, newotherbits;
uint8_t c;
int newdirection;
struct cb_node **wherep, *p;
assert(!((uintptr_t)node & 1)); /* allocations must be aligned */
if (!t->root) { /* insert into empty tree */
t->root = node;
return NULL; /* success */
}
/* see if a node already exists */
p = cb_internal_best_match(t->root, node->k, klen);
/* find first differing byte */
for (newbyte = 0; newbyte < klen; newbyte++) {
if (p->k[newbyte] != node->k[newbyte])
goto different_byte_found;
}
return p; /* element exists, let user deal with it */
different_byte_found:
newotherbits = p->k[newbyte] ^ node->k[newbyte];
newotherbits |= newotherbits >> 1;
newotherbits |= newotherbits >> 2;
newotherbits |= newotherbits >> 4;
newotherbits = (newotherbits & ~(newotherbits >> 1)) ^ 255;
c = p->k[newbyte];
newdirection = (1 + (newotherbits | c)) >> 8;
node->byte = newbyte;
node->otherbits = newotherbits;
node->child[1 - newdirection] = node;
/* find a place to insert it */
wherep = &t->root;
for (;;) {
struct cb_node *q;
size_t direction;
p = *wherep;
if (!(1 & (uintptr_t)p))
break;
q = cb_node_of(p);
if (q->byte > newbyte)
break;
if (q->byte == newbyte && q->otherbits > newotherbits)
break;
c = q->byte < klen ? node->k[q->byte] : 0;
direction = (1 + (q->otherbits | c)) >> 8;
wherep = q->child + direction;
}
node->child[newdirection] = *wherep;
*wherep = (struct cb_node *)(1 + (uintptr_t)node);
return NULL; /* success */
}
struct cb_node *cb_lookup(struct cb_tree *t, const uint8_t *k, size_t klen)
{
struct cb_node *p = cb_internal_best_match(t->root, k, klen);
return p && !memcmp(p->k, k, klen) ? p : NULL;
}
static enum cb_next cb_descend(struct cb_node *p, cb_iter fn, void *arg)
{
if (1 & (uintptr_t)p) {
struct cb_node *q = cb_node_of(p);
enum cb_next n = cb_descend(q->child[0], fn, arg);
return n == CB_BREAK ? n : cb_descend(q->child[1], fn, arg);
} else {
return fn(p, arg);
}
}
void cb_each(struct cb_tree *t, const uint8_t *kpfx, size_t klen,
cb_iter fn, void *arg)
{
struct cb_node *p = t->root;
struct cb_node *top = p;
size_t i = 0;
if (!p) return; /* empty tree */
/* Walk tree, maintaining top pointer */
while (1 & (uintptr_t)p) {
struct cb_node *q = cb_node_of(p);
uint8_t c = q->byte < klen ? kpfx[q->byte] : 0;
size_t direction = (1 + (q->otherbits | c)) >> 8;
p = q->child[direction];
if (q->byte < klen)
top = p;
}
for (i = 0; i < klen; i++) {
if (p->k[i] != kpfx[i])
return; /* "best" match failed */
}
cb_descend(top, fn, arg);
}